KYIV, Ukraine — Since late fall, the number of troops that Russia has dispatched to the borders near Ukraine has been growing. In the first week of January, the United States estimated that they numbered around 100,000. That figure grew to 130,000, and then, on Tuesday, President Biden put the number at 150,000 — with brigades normally based as far away as Siberia joining the force.
Now, even as Russia continues to issue statements saying it is starting to draw down troops, the Pentagon says that another 7,000 soldiers have just joined the ranks near Ukraine and are poised to launch an attack at any moment.
On Wednesday, a senior American official, who refused to be quoted by name, told reporters that far from winding down its deployment, Moscow was adding combatants. Western allies expressed similar rejections of the Russian claims.
The American official directly accused Russia of lying, saying there was new evidence it was mobilizing for war.
The Kremlin spokesman, Dmitri S. Peskov, responded to the accusations on Thursday, saying that Russia was still withdrawing troops, but that it would take time and that he would not get involved in a discussion “over how we move our troops on the territory of our country.”
“This process takes time. It is clear that the military group has been forming for many weeks to take part in the drills, and it is impossible to withdraw these troops in one day,” he said. “They cannot just get lifted in the air and fly away.”
In a reflection of the urgency of the moment, the 27 leaders of the European Union member states were scheduled to meet on Thursday in Brussels for an extraordinary summit to discuss the crisis.
Separately, Defense Secretary Lloyd J. Austin III will meet with the head of NATO, Jens Stoltenberg, in Brussels to discuss the allied effort to counter Russia. Mr. Stoltenberg, echoing other Western officials, said he also saw nothing to support Russia’s claim of a drawdown.
“What we see is that Russian troops are moving into position,” Mr. Stoltenberg said on Wednesday.
With the West essentially accusing Moscow of lying, the outlines of any diplomatic solution to the crisis once again looked very hard to discern.
And even if Russia decides not to send tanks rolling across the border, the enormous deployment — along with alleged cyberattacks and economic pressure — is doing its own harm to Ukraine.
“It feels like we’re watching a slow-motion train wreck happening before our eyes,” Ben Hodges, the former commander of U.S. Army in Europe, wrote on Twitter. “The currently deployed Russian land and naval forces are like a boa constrictor around Ukraine, choking its economy and further threatening its sovereignty.”
Using the threat to Ukraine as a bargaining chip, President Vladimir V. Putin of Russia has made sweeping demands, including the withdrawal of NATO forces from Eastern European countries that used to be under the yoke of the former Soviet Union. The United States and its NATO allies say that will never happen.
Russia has framed the crisis as revolving around its fundamental security. And it says that even the distant prospect of Ukraine joining NATO represents an existential threat.
But the crisis in Ukraine did not begin when Russia issued those demands in December — and it was triggered by security concerns as much as geopolitical ones.
It was in late November 2013 when Ukrainians took to the streets in peaceful protest after Viktor F. Yanukovych, the president at the time, chose not to sign an agreement that would have integrated the country more closely with the European Union.
The protests were brutally repressed, and in the ensuing violence, about 100 civilians — referred to here as the “heavenly hundred” — were killed on Feb. 20 and 21.
Soon after that, Russia annexed Ukraine’s Crimea peninsula and supported a separatist rebellion in the eastern Donbas region that continues to smolder today.
